Yea only my first few REALLY sucked, then I started getting better. Develop your own style and you'll soon be getting high ratings. Tutorials really help, so use the links above.
You will need some good brushes to use, so I suggest: http://www.deviantart.com to download your brushes. Also you will need some renders to put in your sigs, so try here: http://www.clantemplates.com/renders/gallery/